There are many variables in the transfer of energy from a swing of a bat to a batted ball. The mass of the bat and the speed of the bat play an important role in achieving a power swing. The point of impact of the ball along the length of the bat is another factor. Ideally, the impact should be between the center of gravity of the bat and the bat's center of percussion, i.e., the place which when hit by the ball produces no recoil at the batter's wrists, other than a twisting action. Equally important is that the bat must be traveling along the same plane as the ball at the time of impact. This is referred to as a "level" swing.
Achievement of a level swing maximizes the component of force in the desired direction of ball travel after impact. Thus, elimination of a downward "chop" or an "uppercut" in a swing will increase the efficiency of a swing.
Devices which assist a player in developing a level swing are known. U.S. Pat. Nos. 3,794,320 to Salmont, 4,460,172 to Hogan and 4,679,790 to Ham all teach training devices on which a practice ball is extended radially from the top of a shaft for rotation around the shaft. Salmont teaches that the shaft should be inclined so that the ball will be returned to an initial position of rest by gravitational force. The maximum rotation allowed by the Salmont device is 180 degrees. Hogan and Ham teach rotation about a vertical axis and utilize springs which return a ball to an initial position. However, none of these devices provides an indication as to whether a player has utilized a level swing in striking a ball.
U.S. Pat. Nos. 2,818,255 to Ponza and 4,508,339 to Llewellyn teach practice devices in which balls are caused to be rotated about a horizontal axis. An indication of energy transfer is provided because the Ponza and Llewellyn devices include cams that require striking of a ball with sufficient force to overcome both gravitational force and force exerted by a spring which biases cam members together. While the devices provide an improvement, the devices may actually act to develop uppercuts in the swings of users. The camming action of the devices requires that a rotatable upper cam member be lifted axially relative to a shaft. This may be done by a level swing that initiates the camming action, or may be done by a lifting during the swing. The "feel" during impact would encourage the uppercut, since it is not natural for a properly struck ball to be lifted upwardly relative to a level swing. That is, the more natural feel would be one in which the bat would follow the path dictated by the upwardly extending contour of the cam surface of the upper cam member.
It is an object of the present invention to provide a ball-hitting practice device which indicates impact of a ball by a bat swung in a fundamentally correct manner and which more closely simulates the natural "feel" of such an impact.